Coordinated motion of active filaments on spherical surfaces.

Coordinated cilia are used throughout the natural world for micronscale fluid transport. They are often modelled with regular filament arrays on fixed, planar surfaces. Here, we simulate hundreds of interacting active filaments on spherical surfaces, where defects in the cilia displacement field must be present. We see synchronised beating towards or about two defects for spheres held fixed. Defects alter filament beating which causes the sphere to move once released. This motion feeds back to the filaments resulting in a whirling state with metachronal behaviour along the equator.